Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly (unit cell). The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, a predetermined number of the unit cells and the separators are stacked together to form a fuel cell stack.
In the fuel cell, an oxygen-containing gas or the air is supplied to the cathode. The oxygen in the oxygen-containing gas is ionized at the interface between the cathode and the electrolyte, and the oxygen ions (O2−) move toward the anode through the electrolyte. A fuel gas such as a hydrogen-containing gas or CO is supplied to the anode. Oxygen ions react with the hydrogen in the hydrogen-containing gas to produce water or react with CO to produce CO2. Electrons released in the reaction flow through an external circuit to the cathode, creating a DC electric energy.
In the fuel cell, for example, cables as disclosed in Japanese Patent No. 3,251,919 are used for collecting the electrical current at the time of power generation. In the conventional technique, as shown in FIG. 10, a fuel cell stack 2 is provided in a pressure container 1. The fuel cell stack 2 is formed by stacking fuel cells vertically. Components of the fuel cell stack 2 are tightened together using tightening bolts 4 inserted into an upper tightening plate 3a and a lower tightening plate 3b. 
Each of the tightening bolts 4 has a cylindrical shape. A current cable 7a is connected to an upper terminal 5a of the fuel cell stack 2 through an upper cable 6a. The current cable 7a is inserted into one of the tightening bolts 4. A current collecting portion 8a is connected to a lower end of the current cable 7a through a lower cable 6b. 
A current cable 7b is connected to a lower terminal 5b of the fuel cell stack 2, and the current cable 7b is connected to a current collecting portion 8b. The current collecting portions 8a, 8b are exposed to the outside of the pressure container 1.
However, in the conventional technique, heat in the pressure container 1 is transmitted easily through the tightening bolts 4, the lower cable 6b, and the current collecting portion 8a, and a large heat loss occurs. Further, a plurality of tightening bolts 4 are provided on the side portions of the fuel cell stack 2. Thus, the effective space in the pressure container 1 is limited, and the heat capacity is large.
Further, the current collecting portions 8a, 8b are provided at lower positions of the pressure container 1. Therefore, the current collecting structure is constrained. The current collecting portions 8a, 8b cannot be positioned at arbitrary positions, and the layout cannot be designed freely.